Mitigation of wireless transmit/receive unit (WTRU) to WTRU interference using multiple antennas or beams

ABSTRACT

Multiple antenna elements of a WTRU are used to form an adaptive antenna beam pattern for receiving signals in the downlink direction. The WTRU utilizes the formed antenna beam to form a transmission antenna beam for transmitting signals in the uplink direction. In an alternate embodiment, the multiple antenna elements are used to form a plurality of fixed, predetermined antenna beams. The WTRU then selects and switches to the one of the predetermined beams that yields the best downlink reception signals. The WTRU utilizes the selected beam pattern to transmit signals in the uplink direction. In an alternate embodiment, the WTRU receives spectral arrangement information and utilizing this information to avoid transmitting in the direction of spectrally adjacent WRTUs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/025,252 filed Dec. 29, 2004, which claims the benefit of U.S.Provisional Application 60/557,967; filed Mar. 31, 2004, which isincorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention relates to a wireless communication system. Moreparticularly, the present invention relates to mitigating wirelesstransmit/receive unit (WTRU) to WTRU interference in a wirelesscommunication system.

BACKGROUND

Conventional wireless transmit/receive units (WTRUs) typically comprisea single omni-directional antenna that transmits and receives equally inall directions. Utilizing such antennas, however, significantly wastesWTRU resources as most of a WTRU's energy is used to transmit andreceive in directions other than that which is intended. Moresignificantly, this wasted energy is experienced as noise-likeinterference by nearby WTRUs. Such interference is especially momentousin cases where the uplink (UL) frequency of one WTRU is either the sameor near the downlink (DL) frequency of another WTRU. This concept isillustrated in FIG. 1.

FIG. 1 shows a WTRU 102 transmitting omni-directionally. WTRU 104 has anomni-directional receiving beam 112. As the two WTRUs are physically andspectrally close, WTRU 104 experiences significant levels ofinterference and performance degradation. The interference radius 110 ofthe interfering WTRU 102 is determined by its own transmission level,the sensitivity of the receiving WTRU 104, the antenna pattern of WTRU104, and the level of WTRU 104's desired signal. The performancedegradation experienced by WTRU 104 reduces the signal-to-interferenceratio (SIR) and therefore the signal-to-interference-plus-noise ratio ofsignals it receives. If significant enough, the interference 120 causedby WTRU 102 can lead to reduced data rates, loss of connection, and/orpoor signal quality. This phenomenon is known as WTRU to WTRU (mobilestation (MS)-MS) interference.

As described above, WTRUs that utilize omni-directional antennas lackthe technology to preferentially control antenna gain so as to minimizethe transmitting of unwanted signals toward nearby WTRUs. Similarly,utilizing such antennas prevent WTRUs from rejecting interfering signalsemitted from unwanted sources including other nearby WTRUs. Typically,only base stations have been equipped with components and technology tomaximize antenna gain in a desired direction while simultaneouslylimiting the reception of signals in the directions of interferingdevices.

Accordingly, it is desirable to have a WTRU than can maximize antennagain in a desired direction and/or selectively receive signals from adesired direction so as to minimize MS-MS interference.

SUMMARY

The present invention relates to a method and apparatus for mitigatingwireless transmit/receive unit (WTRU) to WTRU interference in a wirelesscommunication system. Multiple antenna elements of a WTRU are used tocontrol the reception gain of the WTRU's antenna. Similar control isapplied to a transmitting antenna to reduce emissions towards nearbyWTRUs.

In an alternate embodiment, the multiple antenna elements are used toform a plurality of fixed, predetermined antenna beams. The WTRU thenselects and switches to the one of the predetermined beams that reducesinterference from nearby WTRUs. The same beam pattern is used whentransmitting to reducing interference caused to nearby WTRUs.

In an alternate embodiment, a WTRU comprises an antenna array andreceives spectral arrangement information. Utilizing this spectralinformation, the WTRU transmits so as to avoid spectrally adjacentWTRUs. Alternatively, the WTRU scans transmission frequencies in searchof high energy sources. The WTRU then determines the transmissiondirections of any high energy (and therefore close) sources andtransmits on its antennas so as to avoid transmitting in the directionof the high energy sources.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from thefollowing description, given by way of example and to be understood inconjunction with the accompanying drawings wherein:

FIG. 1 shows a wireless transmit/receive unit (WTRU) transmittingomni-directionally and interfering with a nearby WTRU;

FIG. 2 illustrates a receiver portion of a WTRU comprising an adaptiveantenna array;

FIG. 3 illustrates a WTRU utilizing an adaptive antenna array;

FIG. 4 illustrates two WTRUs in a reciprocal interference state witheach other;

FIG. 5 illustrates a switched-beam antenna array with its formedpredetermined beams;

FIG. 6 illustrates a WTRU utilizing a switched-beams antenna array; and

FIG. 7 illustrates two WTRUs in an asymmetric interference state witheach other.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the terminology “wireless transmit/receive unit” (WTRU)includes but is not limited to a user equipment, mobile station, fixedor mobile subscriber unit, pager, or any other type of device capable ofoperating in a wireless environment. When referred to hereafter, theterminology “base station” includes but is not limited to a node-B, sitecontroller, access point or any other type of interfacing device in awireless environment.

Although the following embodiments are described in terms of WTRU toWTRU interference, the technology disclosed herein is also applicable tobase station to base station interference scenarios. For example, accesspoint (AP) to AP interference levels, wherein the downlink of a first APinterferes with the uplink of a second AP, can be mitigated utilizingthe technology disclosed herein.

In addition, although beams hereinafter are described primarily in twodimensions, some of the beams may be elevated, having differentazimuths.

In a first preferred embodiment, adaptive antennas, i.e., an adaptiveantenna array, are employed in a WTRU receiver to protect againstinterference from a nearby WTRU. Unlike single antennas utilized byconventional WTRUs, (which approximately have omni-directional antennapatterns (see FIG. 1)), adaptive antenna arrays are capable ofgenerating antenna patterns that are dynamically adjusted in real timeto adapt to current radio conditions. Employed in a WTRU, an antennaarray continually monitors its radio frequency (RF) environment and inparticular, monitors signals received from a servicing base station andany received interference.

A signal processing unit, also in the present WTRU, is utilized tocalculate antenna weights by which signals received in each antennaelement are multiplied. These antenna weights serve to form the WTRU'sbeam pattern. Since the antenna array is constantly monitoring for radiochanges, the signal processing unit is continuously recalculating theantenna weights so as to optimize the WTRU's antenna pattern. Theantenna weights are calculated to either: 1) maximize signal-to-noiseratio (SNR) or signal to noise plus interference ratio (SNIR); or 2)minimize received interference signals; or 3) minimize receivedinterference while maintaining received signal levels at an acceptableconstant. Hereinafter, these three optimization alternatives shall bereferred to collectively as “the three optimization alternatives”. Oneembodiment of a receiver portion of the above described WTRU is shown inFIG. 2.

Antenna elements 202 ₁, 202 ₂, and 202 _(N) in FIG. 2 are arranged in alinear configuration to form antenna array 208. It should be understoodthat linear, circular, planar, and any other 2 or 3 dimensional antennaarrangements can be utilized to form an antenna array. Signals receivedin the antenna array 208 depend on the location of the antennas 202 ₁,202 ₂, and 202 _(N) and on adaptive complex weights w₁, w₂, and w_(N)applied to the received signals. Alternatively, adaptive delays and gaincombinations could be used in lieu of these complex weights. Any methodto adjust these weights w₁, w₂, and w_(N) may be utilized to achieve thethree optimization alternatives discussed above. For example, properlyquantized sets of weights can be tried one after the other until asuitable set is found. Signal processor 220 sends the determined antennaweights, w₁, w₂, and w_(N), to a signal weighting unit 230. In thesignal weighting unit 230, the originally received signals 203 ₁, 203 ₂,and 203 _(N) are combined with calculated weights w₁, w₂, and w_(N),respectively, and then combined to form a single weighted signal 231.

Utilizing adaptive antennas in this manner permits WTRUs to formdirectional beam patterns so as to achieve any of the three optimizationalternatives discussed above. In creating such directional beampatterns, adaptive antennas also create nulls. Nulls are merelydirections of low antenna gain. FIG. 3 illustrates this concept. A WTRU302 is shown having an antenna array 310 that directs a beam pattern 320toward a base station 330. Antenna array 310 also directs nulls 321,approximately toward WTRU 304, a nearby source of WTRU to WTRU (MS-MS)interference. In this example, null beams 321 have the effect of“nulling” out or minimizing interference caused by signals transmittedin the uplink (UL) direction from WTRU 304.

In a second preferred embodiment, an adaptive antenna array is utilizedto select antenna weights so as to achieve one of the three optimizationalternatives discussed above. The WTRU then utilizes antenna weightsderived from the selected weights in order to transmit to a basestation. It is important to note that the derived transmission weightsare chosen such that the essential location and shape of beam createdfor the receiver is kept. As an example, the derived transmissionantenna weights could be the same as the antenna weights selected forreceiving signals.

Transmitting with antenna weights derived as described above isparticularly useful when a transmitting WTRU is in a reciprocalinterference state with a nearby WTRU. WTRUs are described as being in areciprocal interference state when, for example, the UL frequency of afirst WTRU is near or the same as the DL frequency of a second WTRU andthe DL frequency of the first WTRU is near or the same as the ULfrequency of the second WTRU. To illustrate, FIG. 4 shows two WTRUs, 402and 404, in a reciprocal interference state with each other. The ULfrequency f1 of WTRU 404 is very near the DL frequency f1′ of WTRU 402.Similarly, the UL frequency f3 of WTRU 402 is very near the DL frequencyf3′ of WTRU 404. Hence, WTRUs 402 and 404 are in a reciprocalinterference state with each other wherein both WTRUs experience MS-MSinterference when the other is transmitting.

In communication systems that utilize time division duplex (TDD), WTRUsboth transmit and receive signals on the same frequency. In the absenceof alignment, such WTRUs could experience reciprocal interference. Forexample, if two TDD WTRUs are assigned different time slots orfrequencies and their respective frequencies are close or their timingsare not properly aligned or both, these WTRUs may experience reciprocalinterference.

In the same manner described above in the first preferred embodiment,WTRUs in accordance with the present embodiment utilize antenna weightsto optimize the signal quality of desired signals according to one ofthe three optimization alternatives defined above. In the presentembodiment, however, WTRUs derive antenna weights from the selectedreception antenna weights in order to transmit in the UL direction. Byutilizing such derived antenna weights to form directional transmissionbeams, energy directed towards neighboring WTRUs will be reduced servingto protect nearby WTRUs from experiencing MS-MS interference.

In a third preferred embodiment, a switched-beam/switched antenna array(SBSA) is employed in a WTRU receiver to protect against interferencefrom nearby WTRU(s). A SBSA either forms multiple predetermined beams, asubset of which is selected to be used at any given time, or forms a setof beams out of a larger set of predetermined beam positions. It shouldbe noted that one of these formed beam patterns may be anomni-directional beam pattern. An example of these predetermined beampatterns is illustrated in FIG. 5. Switched-beam/switched antenna array510 is shown with its twelve predetermined antenna beams 520 and 522.Beam 520 is highlighted to illustrate that it is the beam that providesthe highest signal quality, perhaps pointing in the direction of a basestation (not shown).

It should be understood that FIG. 5 is solely intended to serve as anexample of the SBSA concept. SBSA systems in accordance with the presentembodiment may have as few as two predetermined antenna beams, possiblyincluding one that has an omni-directional response. The fewer thenumber of antenna beams formed by a SBSA, the wider each such beam willneed to be. The beam width and the number of beams are often determinedby device type and size considerations.

In accordance with the present embodiment, signals are measured in eachof a WTRU's predetermined beams. One of these beams is then selected soas to: 1) maximize the signal to noise plus interference ratio (SNIR) ofthe received signal; or 2) minimize the energy received from nearbyWTRUs; or 3) minimize energy received from nearby WTRUs whilemaintaining a sufficient desired signal level. A switching function thenswitches to the selected one of these fixed beam patterns to receivedesired signals in the downlink direction. In some cases, the selectedbeam may be an omni-directional beam. The continued reduction ofinterference energy received from nearby WTRUs is maintained byfrequently switching between predetermined beam patterns in response tothe WTRU's signal environment. This concept is illustrated in FIG. 6.

Antenna array 610 of WTRU 602 has formed multiple predetermined beams620 and 622. Beam 622 is highlighted to illustrate that it is active anddirected towards base station 630. Accordingly, it has reduced gaintoward nearby WTRU 604.

Utilizing switched-beam antennas in a manner described above permitsWTRUs to select from a plurality of predetermined antenna beams. Inselecting one of these beams, interference received from nearby WTRUs isreduced as shown in FIG. 6. An added advantage to such an implementationis that it minimizes both in-band and out-of-band interference at thesame time.

In a fourth preferred embodiment, a switched-beam antenna array isutilized in a WTRU to minimize MS-MS interference experienced by anearby WTRU, particularly if the WTRUs are in a reciprocal interferencestate. As previously described, WTRUs are in reciprocal interferencewhen, for example, the DL frequency of a first WTRU is near the ULfrequency of a second WTRU while the DL frequency of the second WTRU isnear the UL frequency of the first WTRU (see FIG. 4). In the absence ofproper alignment, WTRUs in a TDD communication system could alsoexperience reciprocal interference.

In the same manner described above in the third preferred embodiment, aWTRU selectively switches between a plurality of predetermined, fixedantenna beams so as to maximize SNIR, minimize energy received fromnearby WTRUs, or minimize energy received from nearby WTRUs whilemaintaining a sufficient desired signal level. In the presentembodiment, however, the WTRU utilizes the same selected antenna beam totransmit in the UL direction. Since the selected beam minimizesinterference energy from unwanted sources, transmitting on this samebeam will minimize the transmission of unwanted energy toward nearbysources. Accordingly, by transmitting in the selected beam direction,interference toward nearby WTRUs is minimized.

In a fifth preferred embodiment, a smart antenna array is utilized in aWTRU to minimize MS-MS interference experienced by nearby WTRU(s),particularly when the WTRUs are in an asymmetric interference state.Hereinafter, the phrase “smart antenna” is used to describe either anadaptive antenna array or a switched-beam/switched antenna array. Forthe purposes of the present embodiment, WTRUs are in an asymmetricinterference state when a first WTRU interferes with the DL reception ofa spectrally adjacent second WTRU. However, the UL transmissions of thesecond WTRU do not interfere with the DL reception of the first WTRU.This concept is illustrated in FIG. 7.

A communication system 700 is shown wherein TDD WTRU 702 has an ULfrequency of f1. WTRU 704, an FDD device, is shown having a DL receptionfrequency spectrally adjacent to that of WTRU 702. As a result, TDDdevice 702 interferes with the DL reception of spectrally adjacent FDDdevice 704. This interference, however, is asymmetric because the ULtransmission frequency f3 of FDD device 704 is spectrally distant fromthe DL frequency f1 of TDD device 702. It should be noted that sinceWTRU 702 is a TDD device, its UL and DL frequency are the same.

As illustrated in FIG. 7, WTRUs such as TDD device 702 canasymmetrically interfere with nearby WTRUs without being aware that suchinterference is occurring. This lack of knowledge is caused because thereception frequency of the interfering WTRU is spectrally distant fromthe UL frequency of the victim WTRU. The present embodiment proposes tominimize such asymmetric interference by providing additionalinformation to interfering WTRUs. An asymmetrically interfering WTRU,(such as TDD WTRU 702 from FIG. 7), is notified of the spectralarrangement in its signal environment. In particular, it is notified ofthe UL frequencies of WTRUs whose DL frequencies are adjacent to its ULfrequency. This information alerts the interfering WTRU as to theexistence of other WTRUs to whom it may possibly cause interference. Theinterfering WTRU then scans those UL frequencies to determine the actuallocations of these WTRUs. The interfering WTRU may determine thelocations of these WTRUs by, for example, searching for high energysignals. A high enough energy level in an UL direction implies that aWTRU is probably nearby and likely to be interfered with. Theinterfering WTRU then accordingly adjust its UL transmission directionutilizing, for example, any of the embodiments described herein, so asto minimize interfering with nearby WTRU(s).

Alternatively, rather than notifying an interfering WTRU as to aspectral arrangement in its signal environment and thus, limiting theWTRUs search, the WTRU can scan all possible frequencies. Although thecomponents of the various embodiments are discussed in terms of separatecomponents, it should be understood that they may be on a signalintegrated circuit (IC), such as an application specific integratedcircuit (ASIC), multiple ICs, discrete components or a combination ofdiscrete components and IC(s).

Similarly, although the features and elements of the present inventionare described in the preferred embodiments in particular combinations,each feature or element can be used alone (without the other featuresand elements of the preferred embodiments) or in various combinationswith or without other features and elements of the present invention.

1. A method of reducing wireless transmit/receive unit (WTRU) to WTRUinterference in wireless communications, the method comprising:transmitting from a first WTRU on a first uplink frequency; receiving atthe first WTRU on a first downlink frequency; receiving at the firstWTRU, information relating to a spectral arrangement of a signalenvironment of the first WTRU, wherein the information includes a seconduplink frequency used by another WTRU; and monitoring the second uplinkfrequency to determine the location of the other WTRU; selecting atransmit beam pattern such that the transmissions from the first WTRUare in a direction other than the direction of the other WTRU.
 2. Themethod of claim 1, wherein monitoring the second uplink frequencycomprises identifying a high energy signal received on the second uplinkfrequency.
 3. The method of claim 1, wherein the transmit beam patternis selected from a predetermined set of transmit beams.
 4. The method ofclaim 1 further comprising applying antenna weights to a plurality ofantenna elements to produce the transmit beam pattern.
 5. The method ofclaim 1, wherein the transmit beam pattern directs a null toward theother WTRU.
 6. The method of claim 1, wherein the information relatingto the spectral arrangement of the signal environment includesinformation relating to another WTRU that has an uplink frequency thatis spectrally adjacent to the downlink frequency of the WTRU.
 7. Awireless transmit/receive unit (WTRU) configured to reduce WTRU to WTRUinterference in wireless communications, comprising: a receiverconfigured to receive data transmissions and information relating to thespectral arrangement of the WTRU environment, including a frequency onwhich another WTRU is transmitting; a signal processor configured toprocess a signal received on the frequency on which the other WTRU istransmitting and determine a direction of the other WTRU; a signalweighting unit configured to calculate antenna weights based on thesignal received on the frequency on which the other WTRU istransmitting; an adaptive antenna array; and a transmitter configured totransmit data in a transmit beam pattern in a direction other than thedirection of the other WTRU.
 8. The WTRU of claim 7, wherein thedirection of the other WTRU is determined based on identifying a highenergy signal received on the frequency on which the other WTRU istransmitting.
 9. The WTRU of claim 7, wherein the transmit beam patternis selected from a predetermined set of transmit beams.
 10. The WTRU ofclaim 7 further comprising applying antenna weights to a plurality ofantenna elements to produce the transmit beam pattern.
 11. The WTRU ofclaim 7, wherein the transmit beam pattern directs a null toward theother WTRU.
 12. The WTRU of claim 7, wherein the WTRU transmits a beampattern in a direction other than the direction of the other WTRU on acondition that the other WTRU is transmitting on an uplink frequencythat is spectrally adjacent to the downlink frequency of the WTRU.